title: Molecular characterization of hprt mutations from Chinese hamster ovary cells treated with 1-, 3-, and 6-nitrosobenzo[a]pyrene.
abstract: 1-, 3-, and 6-nitrobenzo[a]pyrene (nitro-BaP) are environmental contaminants that can be metabolized to genotoxic derivatives by either nitroreduction or ring-oxidation. In this study, we examined the types of mutations produced by the primary nitroreduced metabolites, 1-, 3-, and 6-nitroso-BaP (NO-BaP) in the hprt gene of Chinese hamster ovary cells. RNA from 6-thioguanine-resistant mutants was reverse-transcribed to cDNA and the hprt coding sequence was amplified and sequenced. The mutational patterns produced by the three compounds exhibited extensive similarities: 1) base pair substitutions accounted for 67% (28/42) of 1-NO-BaP, 51% (26/51) of 3-NO-BaP, and 50% (11/22) of 6-NO-BaP mutations; 19-36% of the mutations were exon deletions and 14-18% were frameshifts; 2) most (64-84%) of the simple base pair substitutions occurred at G:C, mainly G:C-->T:A and G:C-->C:G transversions; 3) 98% (46/47) of the simple base pair substitutions at G:C had the mutated dG on the non-transcribed strand and 81% (38/47) were located with the mutated dG flanked 3' by at least one purine; and 4) most simple base pair substitutions (48/62, 77%) occurred in exons 2, 3, and 8 of the hprt gene. Although there were no significant differences among the mutation profiles of the NO-BaPs, a significant difference did exist between the mutation pattern produced by 3-NO-BaP and the mutation pattern previously determined for the ring-oxidized product of 3-nitro-BaP metabolism, trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9, 10-tetrahydro-3-nitrobenzo[a]pyrene. This observation indicates that differences in the structures of closely related adducts can be important enough to have an effect on mutation profiles.
authors.affiliation: National Center for Toxicological Research, Division of Biochemical Toxicology, Jefferson, Arkansas 72079, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Zhan
authors.forename: L H
authors.initials: LH
authors.lastname: Chiu
authors.forename: R H
authors.initials: RH
authors.lastname: Heflich
authors.forename: P P
authors.initials: PP
authors.lastname: Fu
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene / Q000031:analogs & derivatives* / Q000633:toxicity; D001580:Benzopyrenes / Q000633:toxicity*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D009153:Mutagens / Q000633:toxicity*; D009154:Mutation
chemical_list: D001580:Benzopyrenes; D009153:Mutagens; C068647:6-nitrosobenzo(a)pyrene; D001564:Benzo(a)pyrene; C042055:3-nitrobenzo(a)pyrene; C040217:1-nitrobenzo(a)pyrene; D007041:Hypoxanthine Phosphoribosyltransferase